The present invention relates generally to filtration systems and, more particularly, to the removal of oil mist from the hydrogen cooling systems of turbine generators.
The proper performance of a hydrogen-cooled generator depends, inter alia, on the purity of the hydrogen which is circulated throughout its frame and in contact with its conductive components. Typically, hydrogen-cooled generators operate with hydrogen purities well in excess of 95 percent. When hydrogen purity falls below a preselected minimum acceptable value, this condition is typically corrected by purging a portion of the contaminated hydrogen and then refilling the system with pure hydrogen in order to raise the overall purity level of the generator's hydrogen cooling system.
Gas-borne impurities within the hydrogen stream typically consist of styrene, anomine, various other gases which emanate from the epoxies which are used throughout the generator, particulates which are caused by the heating of non-metallic components and oil which exists both in the form of small droplets and gaseous molecules.
The oil, which generally exists as both a mist and a gas within the hydrogen stream, can adversely affect the electrical quality of the generators insulative components and degrade the overall purity of the hydrogen within the generator's cooling system. A reduction in the purity of the hydrogen gas within an electrical generator can have significant deleterious effects on the generator's windage losses and overall efficiency.
A significant and sometimes primary cause for the existance of oil mist within the cooling hydrogen of a turbine generator is the leakage of oil-laden gas from the generator's defoaming tanks into the generator's stator housing through the generator rotor's labyrinth seals. Many types of electrical generators utilize gland seals to contain hydrogen within the generator's frame. These gland seals operate by surrounding a portion of the generator rotor, with a very small gap between the stationary gland seal and the rotating rotor, and injecting a stream of oil into the interface therebetween. The passage of oil in an inboard axial direction prevents hydrogen gas from escaping from within the generator frame through this interface. Upon leaving this interface region of the gland seal, the oil is collected in a defoaming tank and recirculated within the oil system of the generator. These gland seals are located at both the turbine and exciter end of the rotor shaft and are provided with a deflector which prevents the oil from splashing directly against the labyrinth seals as it is ejected from the gland seals. Although the deflectors are generally successful in this function, it is possible that a quantity of oil can be ejected from the gland seals with sufficient velocity to enter the labyrinth seals.
A more severe cause of oil contamination of the hydrogen coolant is the defoaming tank itself. The defoaming tank contains oil in both liquid and vapor form. The defoaming tank contains a quantity of liquid oil at its bottom portion which will eventually be recirculated through the generator's oil system. Above this liquid oil is a mixture of hydrogen gas with oil mist dispersed throughout it and with gaseous oil molecules mixed therethrough. This contaminated gas within the defoaming tank is separated from the cooling hydrogen which exists within the generator's frame by the above-mentioned labyrinth seals. However, if the pressure within the defoaming tank exceeds that of the hydrogen gas on the opposite side of the labyrinth seal, the contaminated gas from above the oil in the defoaming tank can flow through the labyrinth seal into the cooling region of the generator frame and contaminate the much purer quantity of hydrogen used to cool the generator.
Although the pressure of the defoaming tank is intended to be kept at a value less than that of the hydrogen within the generator frame, various causes, including a rise of the oil temperature within the defoaming tank, can cause the pressure within the defoaming tank to exceed that of the hydrogen gas located within the generator. As described above, this increase in gas pressure within the defoaming tank can cause the harmful flow of contaminated gas through the labyrinth seal and into the generator frame causing contamination of the generator's hydrogen cooling system.
The present invention takes advantage of the differential pressures which normally exist within the generator frame in order to direct a portion of the oil-laden mist from within the defoaming tanks through a filtration system which removes a significant percentage of the contaminants from the hydrogen stream and returns the purified hydrogen into the generator's hydrogen circulation system. A pipe is connected in fluid communication with the contaminated gas above the liquid oil in the defoaming tank. This pipe is also connected in fluid communication with an inlet portion of a filtration system. An outlet portion of the filtration system is connected, with appropriate piping, in fluid communication with a portion of the hydrogen cooling system which is known to be at a lower pressure than the gas of the defoaming tank. This differential pressure causes a portion of the contaminated gas to flow from the defoaming tank, through the filtration system and back into the hydrogen cooling system of the turbine generator. Due to this natural flow which is caused by the differential pressures, no additional power is needed to pump the gas through the present invention. The filtration system of the present invention can comprise an air filter, means for coalescing small droplets of oil into larger droplets which can be removed from the gas stream and means for absorbing molecular contaminants which remain in the gas stream after the filtering and coalescing operations.
Since it is typical for a generator to have a defoaming tank at each end of its stator frame, the present invention anticipates the use of two inlet pipes connected to the inlet of the filtration system. Each inlet pipe would connect one of the defoaming tanks with the filtration system with these two inlet pipes being connected in parallel. In order to assure that each defoaming tank is being equally purged of contaminants, the present invention also can incorporate a means for balancing the flow of the two inlet pipes. This balancing means comprises a flow meter for each inlet pipe along with a valve for each pipe so that the flows through the two inlet pipes can be regulated.
Although not a necessity for the proper functioning of the present invention, a flow meter can be attached to the pipe through which the purified hydrogen returns to the generator's cooling system. This flow meter, in conjunction with an appropriate valve for the return pipe, permits both the monitoring and regulation of the hydrogen flow throughout the present invention. The primary advantage of monitoring the gas flow through the filtration system of the present invention is that, for purposes of maintenance, removable filters can be changed when the flow meter indicates a significant drop in flow from levels experienced with clean and unobstructed filters.
It should be apparent that the present invention provides a means for removing inpurities from the hydrogen cooling system of a turbine generator without requiring additional power to be consumed in order to pump the hydrogen gas through its purifying components. It should be further apparent that the present invention does not diminish the quantity of hydrogen of the generator's cooling system but, instead, passes the purified hydrogen back into a low pressure region of the generator frame.